postheadericon Samuel Johnson – Right Visual Cortex Leads

Until the 1960s, observations on the localization and lateralization of language have been based primarily on patients with brain damage of varying severity, location, and etiology. The inevitable uncertainties of clinical results allowed the skeptics to argue that the function of language could not be lateralized in the brain. Definitive evidence supporting the inferences from observations came from studies of neurological patients whose corpus callosum and the anterior commissure was severed as a treatment for medically intractable seizures. . In these patients, the investigators were able to appreciate the function of the two cerebral hemispheres independently, since the major axonal pathways that link was interrupted. Early studies of these so-called split-brain patients were performed by Roger Sperry and his colleagues at the California Institute of Technology in the 1960s and 1970s, and established the hemispheric lateralization of language beyond doubt This work also shows many other functional differences between left and right hemispheres and continues to stand as an extraordinary contribution to the understanding of brain organization. Figure 26.3 Confirmation of hemispheric specialization for language obtained by studying individuals in whom the connections between the right and left hemispheres have been surgically divided. On the one hand, the independent view stereognosis can be used to assess the language ability of each hemisphere in split-brain patients. Objects held in his right hand, which provides somatic sensory information to the left hemisphere, are easily named; objects held in the left hand, however, are not easily named by these patients. Visual stimuli or simple instructions can be given independently to the left or right hemisphere in normal individuals and split-brain. Since the left visual field is perceived by the right hemisphere, a statement briefly presented in the left visual field is determined solely by the right brain. In normal subjects, activation of visual cortex right leads to a hemispheric transfer of visual information by the corpus callosum to the left hemisphere. In split-brain patients, the information presented in the left visual field can not reach the left hemisphere, and patients are unable to produce a verbal report on the stimuli. However, these patients are able to provide a verbal report of stimuli presented in the right visual field. A wide range of hemispheric functions may be evaluated using this method tachistoscopic, even in normal subjects. The list includes some of the functional capabilities of different left and right hemispheres, as reflected in a variety of behavioral tests in split-brain patients.

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